Prevention and remediation of water and  condensate blocks in wells

ABSTRACT

The present invention relates to a method of removing and preventing water and condensate blocks in wells by contacting a subterranean formation with a composition comprising a low molecular weight fluorinated copolymer having perfluoro alkyl moieties which are no longer than C 6 . A fluorinated copolymer of low molecular weight of about 50,000 g/mol and a method of preparing the same are also disclosed.

This application is a divisional application of Ser. No. 13/051,417filed May 18, 2011, entitled “Prevention and Remediation of Water andCondensate Blocks in Wells”, which is a continuation-in-part applicationof Ser. No. 12/437,572 filed May 8, 2009, entitled “Prevention andRemediation of Water and Condensate Blocks in Wells”, which claims thebenefit of the filing date of Provisional Application Ser. No.61/127,029, filed May 9, 2008, entitled “Prevention and Remediation ofWater and Condensate Blocks in Wells”. The entire disclosures are herebyincorporated by reference into the present disclosure.

FIELD OF THE INVENTION

This invention relates to a method for prevention and remediation ofwater block and condensate block in oil and/or gas producingsubterranean formations. In particular, the invention relates tocontacting such subterranean formations with a composition comprising alow molecular weight fluorinated copolymer thereby modifying thewettability of the rock within the subterranean formation and removingand preventing water block and condensate block therein.

BACKGROUND OF THE INVENTION

Typically, hydrocarbon extraction involves drilling a wellbore into anoil and/or gas containing subterranean formation. Hydrocarbon extractionis facilitated by a vast number of interconnected pore throats whichform channels within the subterranean formation thereby allowing flowsof oil and/or gas to the wellbore. The ease of hydrocarbon extraction isdependent upon characteristics of the subterranean formation such asresistivity flow and capillary pressure, both of which are highlydependent upon the number, size, and distribution of unblocked porethroats within the subterranean formation. A common problem encounteredduring typical oil and/or gas extraction, is the decrease ofproductivity resulting from the blockage of pore throats by: 1) water,commonly referred to as “water block”; and/or 2) condensed hydrocarbons,commonly referred to as “condensate block”.

Water block occurs in oil and gas wells when pore throats are blocked byan accumulation of water which may be result of filtrate water fromdrilling mud, cross flow of water from water-bearing zones, water fromcompletion or workover operations, water from hydraulic fracturing, andwater from emulsions. Condensate block occurs in gas wells when porethroats are blocked by an accumulation of liquid hydrocarbons which maybe the result of oil-based drilling mud, hydrocarbon liquids used inworkover operations, and the use of oil-based fracturing fluids.Additionally, the pressure during the extraction of gas often dropsbelow the dew point pressure of the gas causing the gas to condense intoliquid hydrocarbons also resulting in condensate block. Water blocks andcondensate blocks may occur together or independently, leading to adecrease in well productivity and, in certain instances, to completehalt in production.

One method for the prevention or remediation of water blocks and/orcondensate blocks involves modifying the wettability of the rock withinthe subterranean formation wherein the rock is contacted by awettability modifier such that the rock's wettability is modified froman initially oil or water wet state to an intermediate or gas wet state.Proposed wettability modifiers include non-polymeric and fluorinatedpolymers, both of which are disclosed by Panga et al., in U.S. PatentApplication with Pub. No. 2007/0029085.

Unfortunately, previously disclosed non-polymeric surfactants aredisadvantageous for use as wettability modifiers because they sufferfrom low durability and tend to be easily washed away, thereforerequiring repeated treatments. Previously disclosed fluorinated polymersare also disadvantageous for use as wettability modifiers because: 1)they have a high average molecular weight, typically about 140,000 g/molor above; and 2) they have perfluoro alkyl moieties which are C₈ orlonger. This combination of high molecular weight and long perfluoroalkyl moieties translates to a high fluorine content and higher costs.

It would be desirable to discover a fluorinated polymer which can act asa wettability modifier without the aforementioned disadvantages.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a fluorinated copolymer which can act asa wettability modifier for the prevention and remediation of water blockand condensate block in oil and/or gas producing subterranean formationswithout the disadvantages of previously disclosed fluorinated polymers.In particular, the invention provides a fluorinated copolymer having anaverage molecular weight from about 5,000 gram/mol to 50,000 gram/mol,preferably less than about 20,000 g/mol, more preferably less than about10,000 g/mol, and even more preferably less than 2,000 g/mol.Furthermore, the invention provides a fluorinated copolymer havingperfluoro alkyl moieties which are no longer than C₆. This combinationof low molecular weight and shorter perfluoro alkyl moieties translatesto a lower fluorine content and lower costs for use as wettabilitymodifiers for the prevention and remediation of water block andcondensate block in oil and/or gas producing subterranean formations.

The present invention comprises a method for preventing or removingwater block and/or condensate block in a subterranean formationpenetrated by a well bore comprising the step of contacting theformation with an aqueous composition comprising a fluorinated copolymercopolymerized from monomers comprising (preferably consisting of):

(a) from about 30 wt % to about 90 wt % of at least one monomer offormula I:

R_(f)-Q-A-C(O)—C(R)═CH₂  I

wherein

R_(f) is a straight or branched-chain perfluoroalkyl group of from 2 to6 carbon atoms,

R is H or CH₃,

A is O, S or N(R′), wherein R′ is H or an alkyl of from 1 to about 4carbon atoms,

Q is alkylene of 1 to about 15 carbon atoms, hydroxyalkylene of 3 toabout 15 carbon atoms, —(C_(n)H_(2n))(OC_(q)H_(2q))_(m)—,—SO₂—NR′(C_(n)H_(2n))—, or

—CONR′(C_(n)H_(2n))—, wherein R′ is H or an alkyl of from 1 to about 4carbon atoms, n is 1 to about 15, q is 2 to about 4, and m is 1 to about15;

(b) from about 10 wt. % to about 70 wt. % of at least one monomer or amixture of monomers is selected from formula IIA, formula IIB, andformula IIC:

(R₁)₂N—(CH₂)_(r)—Z—C(O)—C(R₂)═CH₂  IIA

(O)(R₃)(R₄)N—(CH₂)_(r)—Z—C(O)—C(R₂)═CH₂  IIB

X⁻(R₅)(R₄)(R₃)N⁺—(CH₂)_(r)—Z—C(O)—C(R₂)═CH₂  IIC

wherein

Z is —O— or —NR₅—; R₁ is an alkyl group of from 1 to about 3 carbonatoms; R₂ is H or an alkyl radical of 1 to about 4 carbon atoms; R₃ andR₄ are each independently an alkyl of 1 to 4 carbon atoms, hydroxyethyl,benzyl, or R₃ and R₄ together with the nitrogen atom form a morpholine,pyrrolidine, or piperadine ring; R₅ is H or an alkyl of 1 to 4 carbonatoms, or R₃, R₄ and R₅ together with the nitrogen atom form a pyridinering; r is 2 to 4; provided that for formula IIA the nitrogen is fromabout 40% to 100% salinized; and

(c) from 0 wt % to about 7 wt % of a monomer of the formula III, IV, Vor VI or a mixture thereof:

CH₂(O)CH₂—CH₂—O—C(O)—C(R₂)═CH₂  III;

Cl—CH₂—CH(OH)CH₂—O—C(O)—C(R₂)═CH₂  IV;

(R₆)OC(O)C(R₆)═CH₂  V;

or

CH₂═CCl₂  VI

wherein

each R₂ is independently H or an alkyl radical of 1 to about 4 carbonatoms, and each R₆ is independently H or an alkyl of 1 to about 8 carbonatoms.

Preferably, the fluorinated copolymer of the present invention has anaverage molecular weight less than about 10,000 g/mol, more preferablyless than about 5,000 g/mol, and most preferably less than about 2,000g/mol.

Preferably, the fluorinated copolymer of the present invention iscopolymerized from a monomer of formula I which is represented byCF₃CF₂(CF₂)_(x)C₂H₄OC(O)—C(H)═CH₂ wherein x=0, 2, and 4.

Preferably, the fluorinated copolymer of the present inventionincorporates a monomer selected from formula IIA wherein the monomerselected is 2-methyl, 2-(diethylamino)ethyl ester.

Preferably, the fluorinated copolymer of the present invention monomerselected from formula V wherein the monomer selected is 2-propenoicacid.

DETAILED DESCRIPTION OF THE INVENTION

Herein, trademarks are shown in upper case.

The term “(meth)acrylate”, as used herein, indicates either acrylate ormethacrylate.

Another advantage of using fluorinated copolymer of the presentinvention as a wettability modifier for the prevention and remediationof water block and condensate block in oil and/or gas producingsubterranean formations is that the fluorinated copolymer's hydrophilicand oleophobic properties can be varied over a wide range for differentapplications and for different subterranean formations by simply varyingthe relative amounts of monomers (a) of formula I and (b) of formula IIAand/or IIB, while still maintaining its properties as an effective waterrepellent and liquid hydrocarbon (oil) repellent.

Preferably monomer (b) of formula IIA is derived from diethylaminoethylmethacrylate by partial or full salinization. The free amine portions ofthe resulting copolymer is then reacted with a salinizing agent such asacetic acid, resulting in the conversion of part or all of the aminemoieties to the corresponding acetate. It must be at least about 40%salinized for adequate solubilizing effect, but may be as high as 100%.Preferably the degree of salinization is between about 50% and about100%. Alternatively, the salinization reaction is carried out on theamine group before the polymerization reaction with equally goodresults. The salinizing group is an acetate, halide, sulfate, tartarateor other known salinizing group.

The proportion of monomer (b) of formula IIA, IIB, IIC or a mixturethereof must be at least about 10% for adequate solubilization. While acopolymer with proportions of this monomer (b) above about 70%, such aproportion will produce polymers with very high viscosity, makingprocessing and handling difficult. Preferably the proportion of monomer(b) of formula IIA, IIB, IIC or a mixture thereof in the copolymer isbetween about 15% and about 45% by weight for the best balance ofhydrophilicity, oleophobicity and viscosity in currently envisionedapplications. Other proportions may be more desirable for otherapplications. All weight percentages are based on the monomer weight asquaternized.

They are prepared by reacting the aforesaid acrylate or methacrylateester or corresponding acrylamide or methacrylamide with conventionaloxidizing agents such as hydrogen peroxide or peracetic acid.

The quaternary ammonium monomers of formula IIC are prepared by reactingthe acrylate or methacrylate esters or corresponding acrylamide ormethacrylamide with a di-(lower alkyl) sulfate, a lower alkyl halide,trimethylphosphate or triethylphosophate. Dimethyl sulfate and diethylsulfate are preferred quaternizing agents.

The presence of monomer (c) of formula III, IV, V, or VI is optional,depending on the particular application for the copolymer. While notwishing to be bound by this theory, it is believed that monomer (c) offormula III and IV acts as a reactive site for the polymer to covalentlybond to the substrate surface. The monomers of formula III, IV, V and VIare prepared by conventional methods known in the art.

The polymerization of comonomers (a), (b) and (c) is carried out in asolvent such as acetone, methylisobutyl ketone, ethyl acetate,isopropanol, and other ketones, esters and alcohols. The polymerizationis conveniently initiated by azo initiators such as2,2′-azobis(2,4-dimethylvaleronitrile). These initiators are sold by E.I. du Pont de Nemours and Company, Wilmington, Del., commercially underthe name of VAZO 67, 52 and 64, and by Wako Pure Industries, Ltd.,Richmond, Va., under the name “V-501.”

EXAMPLES

Examples are carried out using the Berea cores from Cleveland Quarries(Amherst, Ohio) and reservoir sandstone cores from the subsurface fromthe Middle East. The Berea and reservoir core have the same diameter Dof about 2.5 cm, while the length L of Berea is about 15 cm and thelength L of reservoir core is about 10 cm. The permeability of Berea isin a range of 600 mD to 1000 mD. While the permeability of reservoircore is about 2 to about 6 mD. The porosity φ describes the fraction ofvoid space defined by the ratio:

φ=V _(p) /V,  (1)

where V_(p) is the volume of void-space and V is the total or bulkvolume of the porous material, including the solid and void space. Theporosity of Berea (0.21-0.22) is about twice that of the reservoir core(0.11-0.13).

The unit of “PV” (pore volume) is defined as the void volume of a singlecore. The porosity can be alternatively expressed based the bulk densityρ and particle density ρ_(p):

φ=1−ρ/ρ_(p).  (2)

Table 1 shows the relevant data of the cores used in this work. Thesandstone particle density calculated from Eq. (2) is about 2.44 g/cm³for Berea and about 2.61 g/cm³ for reservoir core respectively. Prior tothe experiments, the cores are cleaned by rinse and injection of water,followed by drying in the oven.

TABLE 1 Relevant data of the cores Core type Designation D [cm] L [cm] W[g] φ Berea BYR 2.58 15.1 163.93 0.224 B1 2.58 15.1 153.56 0.220 B2 2.5214.9 151.69 0.205 B3 2.52 14.8 149.49 0.205 B4 2.42 14.5 134.53 0.224 B52.41 14.7 133.90 0.224 B6 2.39 14.7 131.89 0.224 B7 2.45 14.6 138.270.224 B8 2.43 14.6 135.35 0.224 B9 2.43 14.4 133.95 0.224 B10 2.43 14.3128.88 0.224 B11 2.43 14.1 131.14 0.214 B12 2.42 12.8 118.95 0.217 B132.44 14.2 132.09 0.217 B14 2.45 14.4 136.94 0.222 B15 2.45 14.6 138.270.225 B16 2.45 14.1 134.35 0.221 B17 2.45 14.7 139.87 0.224 B18 2.4514.1 134.90 0.222 B20 2.44 14.04 132.52 0.223 B21 2.44 14.26 133.790.224 B22 2.46 14.26 136.95 0.217 B23 2.48 14.67 144.18 0.209 B24 2.4613.10 128.53 0.208 B25 2.46 13.70 134.10 0.208 B18 2.45 14.1 134.900.222 Reservoir R1 2.48 9.72 105.50 0.131 R2 2.48 9.75 106.04 0.134 R32.48 10.48 118.52 0.111 R4 2.48 10.44 118.56 0.105 R5 2.48 10.45 117.160.109

The treatments are carried out by injecting chemical solution into coresand aging at high temperature and high pressure. The wettabilitymodification of cores is evaluated by measurement of contact angle andimbibition test. The liquid mobility is examined by the flow intwo-phase state. By the term “imbibition” as used herein is meant aprocess in which a wetting phase displaces a non-wetting phase in aporous medium.

Mobility in a core is examined via single-phase gas flow, and two-phaseliquid displacing the gas phase. The flow parameters of porous mediawith respect to different fluids are calculated. Applying theForchheimer equation in the steady-state gas flow:

$\begin{matrix}{{\frac{M_{g}\left( {p_{1}^{2} - p_{2}^{2}} \right)}{2\mu_{g}Z\; R\; T\; L\; j_{g}} = {{\beta \frac{j_{g}}{\mu_{g}}} + \frac{1}{k_{g}}}},} & (3)\end{matrix}$

where p₁ and p₂ are the inlet and outlet pressure; M_(g), μ_(g), andj_(g) are molecular weight, viscosity, and mass flux of the gas,respectively; R and Z are the gas constant and the gas deviation factor;T is temperature and L is the core length. The absolute permeability,k_(g), and high velocity-coefficient, β, are determined from theintercept and slope in the plot of M_(g)(p₁ ²−p₂ ²)/(2μ_(g)ZRTLj_(g))vs. j_(g)/μ_(g).

The absolute permeability and high-velocity coefficient are measured. Inthe unsteady-state gas-liquid flow with gas displaced by liquidinjection, the effective and relative permeability of liquid iscalculated at the final steady state using the Darcy expression to thequasi steady-state:

$\begin{matrix}{{{\Delta \; p} = {Q\frac{\mu_{l}}{k_{el}}\frac{L}{A}}},} & (4)\end{matrix}$

to describe the pressure drop, Δp, as a function of the volume flowrate, Q, with the parameters of liquid viscosity, μ_(l), core length, L,cross section area, A, and the effective liquid permeability, k_(el). Itis the so-called ‘effective’ because the core is not 100% saturated withliquid even the pressure drop has reached steady state. Theeffectiveness of the wettability modification from the change of fluidflow parameters after chemical treatment is measured.

The liquid relative permeability k_(rl) is calculated by the ratio ofthe liquid effective permeability to the absolute permeability obtainedfrom single-phase gas flow:

$\begin{matrix}{{k_{rl} = \frac{k_{el}}{k_{g}}},} & (5)\end{matrix}$

Examples are carried out using the Berea cores (B1-B18) from ClevelandQuarries (Amherst, Ohio) and reservoir sandstone cores from thesubsurface from the Middle East. Prior to the tests, the cores arecleaned by rinse and injection of water or normal decane, followed bydrying in the oven. Air is the gas phase in contact angle measurementand imbibition tests. The model liquid is either water or normal decane(oil). The water is either pure water or brine (1.0 wt % NaCl dissolvedin tap water).

2-propenoic acid, 2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylester (CAS 2144-53-8), 2-propenoic acid, 2-methyl-,2-(diethylamino)ethyl ester, acetate (CAS 2397-53-7), and2,2′-azobis(2-methylbutyronitrile) (CAS 13472-08-7) are available fromE. I. du Pont de Nemours and Company, Wilmington, Del. Other reagentsare commercially available, For example, from Aldrich Chemical Co.,Milwaukee, Wis.

Method 1 Chemical Treatment

The wettability of the core was modified by chemical treatment at 140°C. and 1.5×10⁶ Pa (200 psig). The chemical solution of 5 PV is injectedin the nitrogen-saturated core, followed by aging overnight of about 15h. About 20 PV of pure water was then injected to displace the chemicalsolution and wash the core. The injection of chemical solution orwashing water was carried out at a flow rate of 4 cm³/min in Berea.Then, nitrogen (˜30 PV) was injected to drain the liquids from the coreat Δp about 6.9×10⁴ Pa (10 psia) for Berea. The purpose of water washingwas to have an indication of durability of chemical treatment at hightemperature through the examination of the contact angle.

Method 2 Permanency of Treatment

The reaction between rocks and chemicals was studied by analyzing liquidstreams before they enter the rock and after contact with the rock.Qualitative analyses were made by color change in the cores and thesolutions. The chemical adsorption was measured from the gain in thecore weight after treatment. The pH of chemical solutions was measuredby the pH meter (OAKTON, Model pHTestr 30). The automatic temperaturecompensation was built into the pH meter. Through its temperaturesensor, the measurement error caused by the change in the electrodesensitivity due to alterations in the temperature was compensated togive the actual pH reading of the sample. The surface potential of theglass electrode exhibited non-linear behavior vs. the concentration ofH+ or OH− ions in the acid and alkali regions. Three professional pHbuffer solutions at pH=4, 7, 10 (Fisher Scientific), covering the pHrange of the experimental solutions, were used to calibrate the pHmeter. The reproducibility of the pH measurements for the aqueoussolution was about 0.02 units. However due to the low dissociation of H⁺ion in the IPA solution, the pH reading of chemical in IPA solutions hadfluctuations (errors) of about 0.5. The refractive index, density andviscosity of chemical solutions were measured by refractometer (AbbeC-10, accuracy=0.0003), pycometer (Moore-Van Slyke specific-gravitybottle, 2 mL), and viscometer (Ubbelohde capillary, size OB),respectively.

The composition of chemical solutions was analyzed using gaschromatography-mass spectrometry (GCMS) and inductively coupledplasma-mass spectrometry (ICPMS).

Method 3. Contact Angle Measurements

A pipette was used to place a liquid drop on the surface of theair-saturated core at room temperature of about 20° C. The configurationof a sessile liquid drop on the core surface in the ambient air wasmagnified on a monitor screen. Snapshots of the drop image were taken bya digital camera under the proper illumination of light source. Theair-liquid-rock three-phase-contact angle was measured through theliquid phase using the goniometry tool of the software Image ProAnalyzer. In Berea, the liquid drop of water or N-decane (oil) imbibedinstantly into the liquid-wetting untreated core, indicating a contactangle of 0°. As the rock wettability was modified by chemical treatmentto liquid-non-wetting (gas-wetting), the water contact angle, θ_(w),increased to 120°-135° and N-decane (nC₁₀) contact angle, θ_(o),increased to 45°-80°.

Method 4 Spontaneous Imbibition Test

Spontaneous liquid imbibition into the air-saturated cores was monitoredat room temperature of about 20° C. It was performed by immersing theair-saturated core in the liquid while hanging under an electronicbalance. The dynamic process of liquid imbibitions into the core wasstudied by recording the core weight gain with time. The liquidsaturation was calculated as the ratio of the amount of liquid imbibedinto the core to the core pore volume:

$\begin{matrix}{{S_{w} = \frac{\Delta \; {W_{l}/\rho_{l}}}{V_{p}}},} & (6)\end{matrix}$

where ΔW_(l) is the weight gain due to liquid imbibition and ρ_(l) isthe liquid density. The effect of wettability modification was evaluatedby comparing the liquid saturation vs. time before and after treatment.The imbibition rate decreased as the wettability is modified fromliquid-wetting to non-wetting.

Method 5 Fluid Flow Test

Fluid flow tests were conducted to evaluate the effect of wettabilitymodification. FIG. 3 shows the setup. An overburden pressure of 6.9×10⁶Pa (1000 psig) was applied by the syringe pump (ISCO, D series) on thecore inside the core holder (Temco, type HCH). The temperature of thesystem was maintained by a universal oven (Memmert). Gas was injectedfrom the compressed nitrogen cylinder or liquid injection from the inletpump. The inlet pressure and pressure drop were measured by the pressuretransducers (Validyne Engineering), with the accuracy of ˜1.4 kPa (0.2psia) after calibration by the deadweight tester (Ametek). A backuppressure regulator was used to adjust the pressure drop while measuringthe gas flow rate by a flow meter in the range of 1-80 cm³/sec with theaccuracy of about 0.5%. The liquid flow rate was fixed using the inletpump while maintaining the outlet pressure by the receiver pump.

In single-phase gas flow, the inlet and outlet pressures at various gasflow rates were recorded at the steady state. In the two-phase flow whenliquid displaced gas, the liquid was injected at a fixed flow rate intothe gas-saturated core. The transient pressure drop was recorded untilthe steady state was reached.

Example 1 Preparation of Compound A

A 1 L reactor fitted with a stirrer, thermometer and reflux condenserwas charged with: 2-propenoic acid,2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl ester (128.0 g),2-propenoic acid, 2-methyl-,2-(diethylamino) ethyl ester (67.4 g),dodecyl mercaptan (2.4 g), 2,2′-azobis(2-methylbutyronitrile) (VAZO-67,0.98 g) and 4-methyl-2-pentanone (MIBK, 132.0 g). The charged reactorwas then purged with nitrogen for 30 minutes at 30° C. The temperatureof the reactor was then raised to 70° C. and allowed to react withstirring for 16 hours. After 16 hours of reaction time, a 3% acetic acidin water solution (40 g) at 50° C. was slowly added. The MIBK within thereaction mixture was then removed via distillation under atmosphericpressure to give the final product in water which was standardized to30.0% solids (9.3% F content). The number average molecular weight(M_(n)) of the polymer (relative to polystyrene standards) as determinedby gel permeation chromatography was 7,000 Da with a polydispersity(PDI) of 1.5. In this example a low molecular fluoropolymer was achievedbecause the polymerization process was interrupted by the addition ofdodecyl mercaptan.

Example 2 Preparation of Compound C

The same procedure described above for the preparation of Compound A wasemployed, but using of fluoromonomer (a) having the formula:

CF₃CF₂(CF₂)_(x)C₂H₄OC(O)—C(H)═CH₂,

wherein x=0, 2, 4, and 6, with the change in the distribution offluoromonomer (a). A copolymer solution of perfluoroalkylethylmethacrylate, having a weight average molecular weight of approximate10⁴ gram/mol, was obtained, which was designated as Compound C and wasused in the following tests.

Example 3 Preparation of Compound D

Compound D is a fluorinated polydimethylsiloxane fluid, which WACKER65000 VP grafted with 1-perfluorohexyl-ethylene-2-sulfonylchloride: 50gram WACKER 65000 VP, which is available from Wacker Chemie AG, Munich,Germany, reacted with 25 gram of1-perfluorohexyl-ethylene-2-sulfonylchloride in 80 gram methyl isobutylketone (MIBK), at 14° C. A solution of fluorinated polydimethylsiloxane,having a weight average molecular weight of approximate 10³ gram/mol,was obtained. Compound D was used in the following tests.

Example 4 Preparation of Compound E

Compound E is a blend of 5% active ingredient of Compound A preparedabove and 0.25% active ingredient of ZONYL FS-610, a fluorinated telomerbased phosphate ammonium salt in isopropanol, which is available from E.I. du Pont de Nemours and Co., Wilmington, Del. Compound E was used inthe following tests.

Example 5 Preparation of Compound F

Compound F is a blend of 5% active ingredient of Compound A preparedabove and 0.25% active ingredient of ZONYL FS-200, a fluorinated telomerbased amine salt in isopropanol, which is available from E. I. du Pontde Nemours and Co., Wilmington, Del. Compound F was used in thefollowing tests.

Comparative Example 1 Preparation of Comparative Compound A

ZONYL 8740, a polysubstituted methacrylic copolymer, having a weightaverage molecular weight of approximate 10⁵ gram/mol, which is availablefrom E. I. du Pont de Nemours and Co., Wilmington, Del., was used as theComparative Compound A in the flowing tests.

Comparative Example 2 Preparation of Comparative Compound B

ZONYL 8867L, a polysubstituted methacrylic copolymer, having a weightaverage molecular weight of approximate 10⁵ gram/mol, which is availablefrom E. I. du Pont de Nemours and Co., Wilmington, Del., was used as theComparative Compound B in the flowing tests.

Preparation of Aqueous Compositions

The fluoropolymers in Examples 1-5 and Comparative Examples 1-2 weredissolved in isopropanol to a dilution of about 1% wt to about 5% wt.The 1% wt aqueous solutions of Compound A, Compound C, Compound D,Compound E, Compound F, and Comparative Compound.

Contact Angle

FIG. 9. Contact angle of water and nC₁₀ on Berea (A) before and (B)after treatment with Compound E solution (1.05 wt % polymer), and onBerea (C) before and (D) after treatment with Compound F solution (1.05wt % polymer).

The effect of wettability modification was evaluated by measuring thegas-liquid-rock contact angle before and after treatment according tothe Method 3. Contact angle data at the core inlet before and aftertreatment with Compound A-D and Comparative Compound A are shown inTable 2. As the table shows, there seems to be an effect ofconcentration on the increase of the contact angle. The experimentalerror of the measured contact angle was about ˜5°. The increase of watercontact angle was 120°-150° from treatment in Berea; but the increasefor the reservoir core is only 25°-65°. The nC₁₀ contact angle increasewas from 0°-80° for the treated Berea and from 27°-45° for the reservoircore. The treatment with Compound C (2 wt %) and Compound A (1 wt %-5 wt%) increases contact angle the most for water and nC₁₀ in Berea,respectively.

Contact angle data at the core inlet before and after treatment withCompound E-F are shown in Table 3. As the table shows, there seems to bean effect of concentration on the increase of the contact angle. Theexperimental error of the measured contact angle was ˜5°. The increaseof water contact angle was 120°-135° from treatment in Berea. The nC₁₀contact angle increase was 45°-80° for the treated Berea. The contactangle for water was uniform across the core while for nC₁₀; the contactangle change was limited to the inlet of the treated core. The treatmentwith Compound E solution of 3.15 wt % polymer resulted in a highercontact angle measurement for nC₁₀ in Berea, than Compound F. TheCompound E-F induced contact angle increase in the treated Berea coresfor water and nC₁₀, similar to the Compound A, C-D reported in Table 6.

TABLE 2 Contact angle data at 23° C. Contact angle of water and nC₁₀Before After Chemical treatment treatment Change Core Sample Conc. θ_(w)θ_(o) θ_(w) θ_(o) Δθ_(w) Δθ_(o) Type Designation Name Designation [wt %][°] [°] [°] [°] [°] [°] Berea B11 Comparative 0.25 0 0 135 0 +135 0 B4Compound A 1 0 0 120 0 +120 0 B10 0 0 130 0 +130 0 B12 0 0 135 0 +135 0BYR 2 0 0 135 0 +135 0 B2 0 0 135 30 +135 +30 B6 0 0 135 0 +135 0 B9 3 00 135 45 +135 +45 B16 Compound C 1 0 0 135 55 +135 +55 B7 2 0 0 150 50+150 +50 B13 Compound D 1 0 0 135 0 +135 0 B14 Compound A 1 0 0 140 80+140 +80 B17 3 0 0 140 80 +140 +80 B18 5 0 0 140 80 +140 +80 ReservoirR1 Comparative 1 70 0 110 40 +40 +40 R3 Compound A 110 5 135 45 +25 +40R2 2 70 0 135 45 +65 +45 R4 Compound A 1 80 3 135 30 +55 +27 R5 3 70 3135 40 +65 +37

TABLE 3 Contact angle data (~20° C.) Contact angle of water and nC₁₀Chemical solution Before After Polymer treatment treatment Change SampleConc. Chemical θ_(w) θ_(o) θ_(w) θ_(o) Δθ_(w) Δθ_(o) Core Name Solvent[wt %] adsorption [° ] [° ] [° ] [° ] [° ] [° ] B25 IPA IPA 0.00 N/A 0 0120 0 120 0 B22 Compound E 1.05 0.63 0 0 135 60 135 60 B24 3.15 2.02 0 0135 80 135 80 B23 Compound F 1.05 1.08 0 0 135 70 135 70

Imbibition

The results of imbibitions for various new chemicals in Table 4. Thefinal water saturation in spontaneous imbibitions decreases by 81% to93% by treatment with both TLF chemicals. The chemical treatment (withpolymer concentration <3.15 wt %) has little effect on oil imbibition(the imbibition change <6%).

TABLE 4 Imbibition data (~20° C.) Final saturation of water and nC₁₀Chemical solution Before After Polymer treatment treatment Change SampleConc. Chemical S_(w) S_(o) S_(w) S_(o) ΔS_(w)/S_(w) ΔS_(o)/S_(o) CoreName Solvent [wt %] adsorption [%] [%] [%] [%] [%] [%] B25 IPA IPA 0.00N/A 63 67 48 70 25 5 B20 Comparative IPA 0.33 N/A 57 65 50 69 12 6Compound A B22 Compound E IPA 1.05 0.63 60 66 11 70 81 5 B24 3.15 2.0262 66 4 64 93 3 B23 Compound F IPA 1.05 1.08 59 65 8 68 86 4

Permeability

The absolute permeability and high-velocity coefficient before and aftertreatment were measured according to Method 5. The dependence ofpressure drop on gas flow rate is studied using the Forchheimerexpression from Eq. (4) at 140° C. The pressure drop, Δp=p₁−p₂, and theaverage pressure, p=(p₁+p₂)/2 across the core were p about 3.9×10⁵ Paand Δp about 1.6×10⁵ Pa for Berea, and p about 4.7×10⁵ Pa and Δp about7.1×10⁵ Pa for the reservoir core. The measurements of absolutepermeability and high-velocity coefficient before and after treatmentwere presented in Table 5 and Table 6. There was a reduction of absolutepermeability, and an increase in high-velocity coefficient fromtreatment. Generally, the permeability reduction increased andhigh-velocity coefficient decreased with increasing chemicalconcentration. In Table 5, the treatment for Berea with Compound A (1 wt%-5 wt %) seemed to have a negligible effect on permeability. Apermeability reduction of 10% and a high-velocity coefficient increasedby factor of two would have a negligible effect in two phaseperformance. Among all the chemicals, Compound D had the bestperformance in single-phase gas flow.

-   -   In Table 6, the permeability reduction increases and        high-velocity coefficient decrease with increasing Compound E        concentration.

The treatment for Berea with Compound E with 1.05 wt % polymer seemed tohave a negligible effect on permeability. A permeability reduction below10% and a high-velocity coefficient increase by factor of two will havea negligible effect in two-phase performance. Between Compound E andCompound F, Compound E with the least permeability reduction performedthe best in single-phase gas flow, and is comparable to the best one ofCompound A.

TABLE 5 Absolute gas permeability and high-velocity coefficient data at140° C. Absolute permeability and high-velocity coefficient Before AfterChemical treatment treatment Change Core Sample Conc. k_(g) β k_(g) βΔk_(g)/k_(g) Δβ/β Type Designation Name Designation [wt %] [mD] [10⁶cm⁻¹] [mD] [10⁶ cm⁻¹] (%) (%) Berea B11 Comparative 0.25 747 0.10 6810.42 9 319 B10 Compound A 1 957 0.33 811 0.78 15 136 B6 2 911 0.26 7230.49 21 86 B9 3 984 0.27 722 0.57 27 11 B16 Compound C 1 843 0.27 7650.26 9 4 B7 2 875 0.25 681 0.42 22 69 B13 Compound D 1 677 0.29 651 0.314 7 B14 Compound A 1 708 0.28 682 0.32 4 14 B17 3 693 0.33 677 0.42 2 26B18 5 721 0.31 702 0.48 3 53 Reservoir R1 Comparative 1 4.82 253 4.71708 2 180 R3 Compound A 2.36 3605 2.20 8746 7 143 R4 Compound A 1 2.502415 2.46 3334 1 38 R5 3 2.23 3440 2.06 2966 7.5 14

TABLE 6 Absolute gas permeability and high-velocity coefficient data(140° C.) Absolute permeability and high-velocity coefficient Chemicalsolution Before After Polymer treatment treatment Change Sample Conc.k_(g) β k_(g) β Δk_(g)/k_(g) Δβ/β Core Name Solvent [wt %] [mD] [10⁶cm⁻¹] [mD] [10⁶ cm⁻¹] (%) (%) B25 IPA 0.00 667 0.23 570 0.28 14 23 B22Compound E IPA 1.05 687 0.22 698 0.23 2 4 B24 Compound F IPA 3.15 6400.18 598 0.31 6 79 B23 1.05 614 0.14 550 0.18 10 23FIG. 15. Pressure drop vs. pore volume before and after treatment withchemicals: Berea, 140° C. (A) Compound E and Compound F (B) Compound A,E, F and Comparative compound A.

Two-phase flow testing by water displacement of gas was performed. Waterwas injected into the nitrogen-saturated cores at a fixed flow rate of 6cm³/min for Berea at 140° C. and the outlet pressure of 1.5×10⁶ Pa (200psig). The pressure drop across the untreated and treated core wasmonitored with time.

The effective and relative permeability were calculated fromsteady-state pressure drop using the Darcy law. The results are shown inTable 7 and Table 8. The chemical treatment decreased the pressure drop,and increased the effective and relative permeability for both the Bereaand reservoir cores. The treatment effectiveness was evaluated bycalculating the changes in the effective permeability and relativepermeability. Both Δk_(ew)/k_(ew) and Δk_(rw)/k_(rw) decreased withincreasing Comparative Compound A concentration, but Compound A had anoptimum concentration at 3 wt %. Among all the chemicals, Compound D hadthe best performance in increasing the water effective permeability inBerea, followed by Compound A. Compound D was the only chemicalcontaining siloxane, which was perhaps contributing to its superiorperformance to repel water. However for the reservoir core, ComparativeCompound A was more effective than Compound A. Between Compound E andCompound F, Compound E (1.05 wt % polymer) with the largestΔk_(ew)/k_(ew) and Δk_(rw)/k_(rw) performed the best in water injectiontest. All the results for k_(rw) in Table 7 and Table 8 provided astrong indication that the chemical treatment changed the core surfacefrom hydrophilic to hydrophobic resulting in an increase in watermobility.

TABLE 7 Effective water permeability and relative permeability data at140° C. Effective and relative permeability Before After Chemicaltreatment treatment Change Core Conc. k_(ew) k_(ew) Δk_(ew)/k_(ew)Δk_(rw)/k_(rw) Type Designation Sample Designation [wt %] [mD] k_(rw)[mD] k_(rw) (%) (%) Berea B10 Comparative 1 197 0.21 393 0.48 100 136 B6Compound A 2 223 0.24 334 0.46 50 89 B9 3 261 0.27 365 0.51 40 90 B16Compound C 1 214 0.25 415 0.54 94 114 B7 2 262 0.30 366 0.54 40 80 B13Compound D 1 152 0.22 376 0.58 147 157 B14 Compound A 1 176 0.25 3790.56 116 124 B17 3 153 0.22 415 0.61 142 148 B18 5 219 0.30 390 0.56 7882 Reservoir R1 Comparative 1 1.33 0.28 2.00 0.42 50 53 R3 Compound A0.77 0.32 0.91 0.41 19 28 R4 Compound A 1 0.96 0.38 1.01 0.41 5 6 R5 30.93 0.42 1.09 0.53 17 27

TABLE 8 Effective water permeability and relative permeability data(140° C.) Effective and relative water permeability Chemical solutionBefore After Polymer treatment treatment Change Sample Conc. k_(ew)k_(ew) Δk_(ew)/ Δk_(rw)/k_(rw) Core Name Solvent [wt %] [mD] k_(rw) [mD]k_(rw) k_(ew) (%) (%) B25 IPA 0.00 266 0.40 320 0.56 20 41 B22 CompoundE IPA 1.05 252 0.37 441 0.63 75 72 B24 3.15 259 0.41 382 0.64 47 57 B23Compound F IPA 1.05 247 0.40 341 0.62 38 54

In summary, the examples demonstrated the wettability modification ofvarious rock samples from liquid-wetting to intermediate gas-wetting bythe method of the present invention wherein the rock samples arecontacted with a composition comprising a low molecular weightfluorinated copolymer in accordance with the invention. The wettabilitymodification increased the contact angle of liquid drops on the core,and decreased the spontaneous imbibition. The effect of wettabilitymodification on liquid mobility was pronounced in the gas-water system.The adsorption of the fluorochemical onto the core surface hasnegligible effect on the absolute permeability for the chemicals withsmall molecular weight.

Thus, while there have been described what are presently believed to bethe preferred embodiments of the present invention, those skilled in theart will realize that other and further modifications can be made to theinvention without departing from the true spirit of the invention, suchfurther and other modifications are intended to be included hereinwithin the scope of the appended claims.

What is claimed is:
 1. A fluorinated copolymer copolymerized frommonomers comprising: (a) from about 30 wt % to about 90 wt % of at feastone monomer of formula I:R_(f)-Q-A-C(O)—C(R)═CH₂  I wherein R_(f) is a straight or branched-chainperfluoroalkyl group of from 2 to 6 carbon atoms, R is H or CH₃, A is O,S or N(R′), wherein R′ is H or an alkyl of from 1 to about 4 carbonatoms, Q is alkylene of 1 to about 15 carbon atoms, hydroxyalkylene of 3to about 15 carbon atoms, —(C_(n)H_(2n))(OC_(q)H_(2q))_(m)—,—SO₂—NR′(C_(n)H_(2n))—, or —CONR′(C_(n)H_(2n))—, wherein R′ is H or analkyl of from 1 to about 4 carbon atoms, n is 1 to about 15, q is 2 toabout 4, and m is 1 to about 15; (b) from about 10 wt % to about 70 wt %of at least one monomer or a mixture of monomers is selected fromformula IIA, formula IIB, or formula IIC:(R₁)₂N—(CH₂)_(r)—Z—C(O)—C(R₂)═CH₂  IIA(O)(R₃)(R₄)N—(CH₂)_(r)—Z—C(O)—C(R₂)═CH₂  IIBX⁻(R₅)(R₄)(R₃)N⁺—(CH₂)_(r)—Z—C(O)—C(R₂)═CH₂  IIC wherein Z is —O— or—NR₅—; R₁ is an alkyl group of from 1 to about 3 carbon atoms; R₂ is Hor an alkyl radical of 1 to about 4 carbon atoms; R₃ and R₄ are eachindependently an alkyl of 1 to 4 carbon atoms, hydroxyethyl, benzyl, orR₃ and R₄ together with the nitrogen atom form a morpholine,pyrrolidine, or piperadine ring; R₅ is H or an alkyl of 1 to 4 carbonatoms, or R₃, R₄ and R₅ together with the nitrogen atom form a pyridinering; r is 2 to 4; provided that for formula IIA the nitrogen is fromabout 40% to 100% salinized; and (c) from 0 wt % to about 7 wt % of amonomer of the formula III, IV, V or VI or a mixture thereof:CH₂(O)CH₂—CH₂—O—C(O)—C(R₂)═CH₂  III;Cl—CH₂—CH(OH)CH₂—O—C(O)—C(R₂)═CH₂  IV;(R₆)OC(O)C(R₆)═CH₂  V;orCH₂═CCl₂  VI wherein each R₂ is independently H or an alkyl radical of 1to about 4 carbon atoms, and each R₆ is independently H or an alkyl of 1to about 8 carbon atoms, wherein the fluorinated copolymer has anaverage molecular weight less than about 50,000 g/mol, wherein anyperfluoroalkyl moieties present in the fluorinated copolymer are nolarger than 6 carbon atoms long.
 2. The fluorinated copolymer of claim 1having an average molecular weight less than about 20,000 g/mol.
 3. Thefluorinated copolymer of claim 1 having an average molecular weight lessthan about 10,000 g/mol.
 4. The fluorinated copolymer of claim 1,wherein the monomers of the fluorinated copolymer are copolymerized inthe presence of dodecyl mercaptan.
 5. A method of preparing thefluorinated copolymer of claim 1 comprising reacting2-methyl-3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl ester,2-methyl-,2-(diethylamino) ethyl ester, and dodecyl mercaptan underconditions suitable to make the fluorinated copolymer having an averagemolecular weight of about 20,000 g/mol.